Study Groups Chapter 11

Chapter 10 Review

100

The types of intermolecular forces in a substance are identical whether it is a solid, a liquid, or a gas. Why then does a substance change phase from a gas to a liquid or to a solid?

Heat (Kinetic Energy)

Recall: "Tug of war" analogy

200

List each type of IMF in order from weakest to strongest. For each, draw an example molecule that exemplifies the IMF. 

LDF, Dipole-Dipole, Hydrogen "bridge", Ion-Dipole

300

Which Molecule would have:

1) the highest boiling point

2) The highest heat of vaporization

3) The highest rate of vaporization

Be prepared to explain why. 

Molecules: 

A: H20

B: C5H12

C: OHCH2CH2OH

All can be predicted with IMF. 

1,2 --> C (Highest IMF)

3 ---> B (Lowest IMF)

400

Name the phase transition that is occurring from:

A. Point 4 to Point 2

B. Point 5 to Point 2

C. Point 4 to Point 3

D. Point 1 to Point 3

A. Freezing

B. Condensation

C. Deposition

D. No Phase Change

500

Carbon tetrachloride, CCl4, was once used as a dry cleaning solvent, but is no longer used because it is carcinogenic. At 57.8 °C, the vapor pressure of CCl4 is 1064 torr, and its enthalpy of vaporization is 33.05 kJ/mol. Use this information to estimate the normal boiling point for CCl4. Provide your answer in Celsius.

49 degrees Celsius

11.1: Dissolution

100

How do solutions differ from compounds? From other mixtures?

A solution can vary in composition, while a compound cannot vary in composition. Solutions are homogeneous at the molecular level, while other mixtures are heterogeneous.

200

5.

Indicate the most important types of intermolecular attractions in each of the following solutions:

(a) CH3OH(g) in H20(l)

(b) NO(l) in CO(l)

(c) Cl2(g) in Br2(l)

(d) HCl(g) in benzene C6H6(l)

(e) Methanol CH3OH(l) in H2O(l)

SOLUTION- HOMOGENOUS

Most Important- What interactions can lead to a homogenous solution?

A- H Bonding

B- Dipole-Dipole

C- LDF

D- LDF

E- H-Bonding

300

Predict whether each of the following substances would be more soluble in water or in a hydrocarbon such as heptane (C7H16):

(a) vegetable oil (nonpolar)

(b) isopropyl alcohol (polar)

(c) potassium bromide (ionic)

"Like Dissolves Like"

Water -> We know is polar

C7H16 -> Only nonpolar bonds -> Non-polar

A) Heptane (LDF)

B) Water (Dipole-Dipole)

C) Water (Ion-Dipole interactions)

400

When KNO3 is dissolved in water, the resulting solution is significantly colder than the water was originally.

(a) Is the dissolution of KNO3 an endothermic or an exothermic process?

(b) What conclusions can you draw about the intermolecular attractions involved in the process?

(c) Is the resulting solution an ideal solution?

(a) The process is endothermic as the solution is consuming heat. 

(b) Attraction between the K+ and N⁢O3⁢− ions is stronger than between the ions and water molecules (the ion-ion interactions have a lower, more negative energy). Therefore, the dissolution process increases the energy of the molecular interactions, and it consumes the thermal energy of the solution to make up for the difference. 

(c) No, an ideal solution is formed with no appreciable heat release or consumption.

500

ENDOTHERMIC VS EXOTHERMIC DISSOLUTION PROCESSES

Heat is released when some solutions form; heat is absorbed when other solutions form. Provide a molecular explanation for the difference between these two types of spontaneous processes.

Bonus: What symbol do we use to represent this? When is it positive? When is it negative?

Heat is released when the total intermolecular forces (IMFs) between the solute and solvent molecules are stronger than the total IMFs in the pure solute and in the pure solvent. Breaking weaker IMFs and forming stronger IMFs releases heat. Heat is absorbed when the total IMFs in the solution are weaker than the total of those in the pure solute and in the pure solvent: Breaking stronger IMFs and forming weaker IMFs absorbs heat.

11.2: Electrolytes/molality

100

Which of the following is a nonelectrolyte when dissolving in water?

A) HCl B) NaNO3 C) CH3CH2OH D) CuCl2 E) NaOH

C) CH3CH2OH

Covalent- Will not ionize in water. 

200

1. HCl, KOH, LiCl, and KI are ALL classified as________.

A) nonelectrolytes 

B) weak electrolytes 

C) strong electrolytes 

D) acids

C) Strong electrolyes

Strong: Completely dissolves (Ionizes)

300

A solution is 0.0480 m LiF. What is the molarity of the solution if the density is 1.10 g/mL?

A) 0.0441 M B) 0.0480 M C) 0.0436 M D) 0.0528 M E) 0.0417 M

D) 0.0528 M

400

At 20°C, a 2.32 M aqueous solution of ammonium chloride has a density of 1.0344 g/mL. What is the molality of ammonium chloride in the solution? The molar mass of NH4Cl is 53.50 g/mol.

A) 2.55 m B) 0.0449 m C) 2.32 m D) 0.446 m E) 12.00 m

A) 2.55 m

LO #5. Define, solve for, and convert between: Molarity, molality and mole fraction

500

What is the molarity of a saturated solution of potassium sulfate (K2SO4) if the solubility is 13 g per 100 g H2O at 25°C? The density of the solution is 1.1 g/mL. The molar mass of potassium sulfate is 174.27 g/mol.

A) 1.1 M B) 0.14 M C) 0.82 M D) 0.73 M E) 0.96 M

D) 0.73 M

11.3: Solubility

100

Which statement is correct?

A) A saturated solution involves a dynamic equilibrium between dissolving and recrystallization.

B) A saturated solution always contains a high concentration of solute.

C) The solubility of solids always decreases with increasing temperature.

D) The solubility of a gas usually increases with increasing temperature.

A) A saturated solution involves a dynamic equilibrium between dissolving and recrystallization.

Bonus: Define an unsaturated, saturated, and supersaturated solution

200

A saturated solution was made by dissolving a solid into a liquid. Which of the following is NOT

TRUE in a dynamic equilibrium describing the saturated solution?

A) Concentration of dissolved solute remains constant.

B) Rate of dissolving is double the rate of crystallization.

C) Solid dissolves into solution.

D) Solid crystallizes from solution.

E) Quantity of undissolved solute remains constant

B) Rate of dissolving is double the rate of crystallization.

BONUS: 

Why Can't this be true? What kind of solution would it be (unsaturated or supersaturated) if it were true?

Why are C and D not false?

300

Determine if each point (A-D) is saturated, unsaturated, or supersaturated on the solubility curve (white board)

White Board (Solubility Vs Temperature)

400

Calculate the molality of a solution that is prepared by mixing 25.5 mL of CH3OH (d = 0.792 g/mL) and 387 mL of CH3CH2CH2OH (d = 0.811 g/mL).

A) 0.630 m B) 0.812 m C) 1.57 m D) 2.01 m E) 4.98 m

D) 2.01 m

500

Determine the vapor pressure of a solution at 25°C that contains 76.6 g of glucose (C6H12O6) in 250.0 mL of water. The vapor pressure of pure water at 25°C is 23.8 torr. (Density of water is 1.0 g/mL). Molar mass of glucose = 180.156 g/mol, water = 18.016 g/mol.

A) 70.8 torr B) 72.9 torr C) 23.1 torr D) 22.9 torr E) 7.29 torr

C) 23.1 torr

Raoults Law

11.4: Colligative Properties

100

0. Which statement is NOT true regarding colligative properties?

A) Raoult's Law describes the vapor pressure above a solution.

B) Since the vapor pressure of the solvent is lowered by a nonvolatile solute, the boiling point of

the solution is higher.

C) The magnitude depends on the concentration of solute.

D) The magnitude depends on the identity of the solute.

E) The magnitude depends on whether the solute is an electrolyte or not.

D) The magnitude depends on the identity of the solute.

200

What is the expected freezing point of a 0.50 m solution of Li2SO4 in water? Kf for water is 1.86°C/m.

A) −0.93°C B) −1.9°C C) −2.8°C D) −6.5°C

C) −2.8°C

300

30. Which of the following solutions will have the lowest freezing point?

A) 0.0100 m NaCl

B) 0.015 m MgCl2

C) 0.035 m CH3CH2CH2OH

D) 0.0100 m Li2SO4

B) 0.015 m MgCl2

400

 If one mole of each is dissolved in 1.00 L of water, which will lower the vapor pressure the most?

A) C3H7OH B) NaNO3 C) MgCl2 D) C12H22O11

C) MgCl2

500

The normal boiling point of pure benzene is found to be 80.10°C. What is the approximate molar mass of a nonionizing substance if a solution of 3.550 g of the substance dissolved in 100. g of benzene has a normal boiling point of 80.19 oC? Kb = 5.12 oC/m for benzene, C6H6.

A) 2020. g/mol 

B) 500. g/mol 

C) 20. g/mol 

D) 20,000. g/mol

A) 2020. g/mol